Previously cores for forming jackets for coupling liquids around cylinders such as in the blocks of internal combustion engines had printout portions in their cylindrical sides and not at the ends thereof. Furthermore, if there was any taper at all in the surfaces of the core, it was converging from the center side printout in both axial directions. Also there was no connection between the sides of the cores between cylinders of a plural cylinder core, so that the only connection between opposite sides of the plural cylinder core was at the ends of the core.